22 PW DEC2021
THE BIG PICTURE
By Sterling Anthony, CPP, Contributing Editor
A Look at Metal Lug Closures A lug closure’s short profile and simple appearance belie the Also known as lug lids, lug caps, and engineering and tight tolerances necessary for an adequate pairing twist caps, lug closures are the choice with the glass container. Lug closures are designated by an inside for a variety of products that are heatdiameter (in millimeters), joined by a hyphen to a standardized processed and hot-filled in glass jars. Lugs description code (designating whether the closure is of the 2-lug, are the equally spaced tabs around the 4-lug, or 6-lug variety). The description code, in turn, corresponds to a skirt (under-rim) of the closure. Their purpose is to interlock with specific finish (threaded neck) of a container. What’s to be appreciated the interrupted tread of the container’s finish (neck). Due to that is that the manufacture of lug closures entails more than just interlocking, lug closures can be applied or removed with less than a stamping them out on a machine press. If closures arrive at the user’s full turn. Continuous-tread (C-T) closures, by contrast, interlock with facility “out of spec,” subsequent operations will be all for naught. the continuous thread of the container’s finish and require at least a At the capping station, the closures are full turn to apply or remove. On the inside of lug closures is a A lug closure’s short profile and positioned and torqued at programmed speeds. However, immediately preceding compound (typically plastisol), essential in simple appearance belie the those operations, it’s advisable to apply effecting a hermetic seal. When the closure is applied, the compound compresses engineering and tight tolerances heat to soften (not melt) the sealing compound, so that it spreads more around the lip (land) of the container, necessary for an adequate uniformly around the container’s land. filling any void between the container’s lip pairing with the glass container. Another factor impacting seal integrity and the underside of the closure. is the amount of headspace. Too little Heat-processed high-acid foods, such headspace runs the risk of product getting into the sealing areas. as sauces, soups, marinades, and jams/jellies/preserves, are heatToo much headspace runs the risk of it not getting sterilized. The processed, hot-filled into glass jars, and crowned with lug closures. sterilization of the headspace (and the interior of the lug closure) is Processing, filling, and capping are components of a system for achieved by the temperature of the contents (typically 190° to 200°F), producing shelf-stable products. Processing and filling must be done when the filled and capped container is inverted. The duration of under strictly controlled temperature setting to destroy harmful the inversion should be for one minute or longer, during which, microorganisms. After that, the lug closure becomes the main agent the container should be in motion toward the location where the in maintaining shelf-stability until the container is opened. container is turned right-side-up. After all, a hermetic seal on nonLug closures fulfill all the functions of packaging: containment/ sterile contents serves no purpose. protection, communication, and convenience/utility. Containment/ Even the cooling period influences seal integrity. As the contents protection has been addressed by preceding comments. cool, a vacuum is created, applying greater hold-down on the lug Communication can be had with printing on the top and around the closure. A loss of vacuum (which only is intended to occur at the side, conveying brand name, product line variety, and promotional consumer’s in-home removal of the lug closure) is evidenced by the claims. Also under communication is safety information, such as aforementioned pop-up of the safety dimple/button. refrigerate after opening. Another type of safety communication As for capping stations, there is no universal configuration. Capping warns against purchasing the product if the center-located dimple/ stations differ in terms of machines and button has popped up (which happens models. Nonetheless, they all encounter when the hermetic seal has been broken). problems that happen with varying freConvenience/utility accrues from the twistMarch 21-23, 2022 Pennsylvania Convention Center quency. One such problem is loose engageon-and-off feature and can be enhanced Philadelphia, PA USA ment between lugs and threads. Another is with ribbed sides for better gripping. closures that sit cocked, like a fedora slantGiven that glass containers and metal ed on someone’s head. One more is flatlug closures are complete barriers, the tened or crushed lugs. Yet another is enammost likely cause of lost sterility is a el that’s been stripped from the underneath poor seal. When experienced on a large Interested in the latest closure of the closure. These and other problems scale, lost sterility can result in rejected tech? Don’t miss PACK EXPO East can result from a variety of causes, thereby shipments or even a product recall. It where a wide range of closures and complicating troubleshooting. But without behooves a brand-owner, therefore, to containers will be demonstrated. a fast and accurate identification and soluhave quality-assurance measures geared to tion, output will be slowed at best, or even achieving quality seals. REGISTER TODAY packexpoeast.com worse, stopped. PW It starts with the choice of supplier.
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